JP2002063766A - Information reproducing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reproduction stability of the ADIP(address in pregroup) signal of an MD(mini disk). SOLUTION: The center frequency f0a of the passband of a band pass filter which extracts a wobble signal component is set more highly than the average frequency fs of a reproduction wobble signal. As a result, the S/N ratio (SNa) of the wobble signal can be improved compared with a conventional S/N ratio (SNb), and thus the stability of reproduction operation of the ADIP signal can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information reproducing apparatus for reproducing modulated information data from an optical disk, a magneto-optical disk, a magnetic disk or the like.

[0002]

2. Description of the Related Art In recent years, recordable optical disk devices such as a mini disk (hereinafter abbreviated as MD) and a DVD-RAM have been actively developed. Hereinafter, as an example of such a conventional recordable optical disk apparatus, an information reproducing apparatus that reproduces address information data from an MD will be described with reference to the drawings.

The MD format has a read-only ROM.
There are discs and recordable RAM discs. In an MD RAM disk, address information indicating an absolute position on the disk is bi-phase modulated and further FM-modulated, and recorded in advance in the disk as a small meandering wobble of a recording track (hereinafter referred to as a wobble). . This is called an ADIP (address in pregroove) signal. The reproducing apparatus detects the wobble signal component of the recording track, performs FM demodulation of the wobble signal component, and further performs biphase demodulation, thereby reproducing the address information on the disk.

FIG. 4 is a block diagram showing main components of an information reproducing apparatus using a conventional technique. In FIG.
1 is a disk (MD), 2 is a motor for rotating the disk 1, 3 is a driver for supplying driving power to the motor 2, 4 is an FG (frequency generator) that generates a pulse signal according to the rotation speed of the motor 2. Generator 5) is a rotation control means for controlling the motor 2 to a predetermined rotation speed based on the output signal of the FG 4. Reference numeral 6 denotes an optical pickup, which is a semiconductor laser that generates a light beam, an objective lens that focuses the light beam on the recording surface of the disk 1, and an objective lens that is perpendicular to the recording surface of the disk 1 and perpendicular to the recording tracks. And a light receiving element for detecting reflected light from the disk 1 and a circuit element associated therewith to detect an information signal recorded on the recording surface of the disk 1 and to detect a light beam spot and the disk 1 And a relative position error signal (tracking error signal) between the light beam spot and the recording track of the disk 1 are detected. 7 is a wobble signal detecting means for detecting a wobble component of a recording track of the disk 1 based on an output of the optical pickup 6;
Reference numeral 8 denotes a band-pass filter which receives an output of the wobble signal detecting means 7 and passes a signal in a predetermined frequency band.
Is an address demodulating means for performing FM demodulation and biphase demodulation using the output of the band pass filter 8 as input, and demodulating address information (ADIP signal) recorded on the disk 1.

[0005] The operation of the conventional information reproducing apparatus having the above-described configuration will be described below.

First, the rotation control means 5 generates a signal corresponding to the number of rotations of the motor 2 based on the pulse signal generated by the FG 4 and compares it with a predetermined target value to generate a rotation error signal. , And drives the motor 2 by the driver 3 to control the disk 1 to a predetermined rotation speed. In the MD, a digitized music information signal is EFM-modulated and recorded on a disk. This signal is recorded at a CLV (constant linear velocity). For this reason, the target rotation speed of the rotation control system using the FG is determined based on the address information read from the disk.
The target rotation speed is increased near the inner circumference of the disk, and is varied so as to gradually decrease as the disk moves toward the outer circumference. This makes it possible to always read the information signal at a constant linear velocity (CLV) while keeping the reproduction linear velocity near a predetermined reference value.

A focus error signal and a tracking error signal output from the optical pickup 6 are input, and these signals are subjected to filter processing such as phase compensation and low-frequency compensation by servo means (not shown). The actuator of the optical pickup 6 is driven based on the output signal to move the objective lens so that the light beam spot follows the recording surface of the disk 1 (focus control) and also follows the recording track (tracking control).

Next, the wobble detecting means 7 detects the wobble component of the recording track of the disk 1. This will be described below with reference to FIGS.

FIG. 2 is a schematic diagram showing a wobble of a recording track on an MD RAM disk. In FIG. 2, a indicates a light beam spot focused on the recording surface of the disk 1, and an arrow indicates a direction in which the light beam spot a relatively moves on the recording surface of the disk 1 as the disk 1 rotates. . If the tracking control is normally performed, the light beam spot a is correctly positioned on the target track as shown in FIG. 2 and advances in the direction of the arrow. The frequency band that the tracking control follows is usually about 1 to 2 kHz, but the wobble component is set to a much higher frequency than this (in MD, when the reproduction is performed at a normal linear velocity, the average value is about 22. kHz). 05 kHz), the tracking control system hardly follows the wobble, which is a minute meandering of the recording track, and the light beam spot a advances straight in the direction of the arrow in FIG. Therefore, the wobble component becomes a residual component of the tracking error almost as it is. That is, the wobble signal component can be easily detected by detecting the tracking error component when the tracking control is normally performed in the wobble detection unit 7.

A method of detecting a tracking error will be described below with reference to FIG. FIG. 3 is a schematic diagram showing a general method for detecting a tracking error signal. In FIG. 3, a is a light receiving element for detecting the reflected light from the disk 1, and is indicated by a dividing line substantially perpendicular to the direction (horizontal axis direction in FIG. 3) corresponding to the radial direction of the disk 1.
Area a1 and a2. b is a subtraction circuit for detecting the difference between the outputs of the divided areas a1 and a2 of the light receiving element a, and c is the disk 1 on the light receiving element a.
The reflected light beam spot d indicates the light amount distribution of the reflected light beam spot c in the direction corresponding to the radial direction of the disk 1. The light amount distribution (d in FIG. 3) of the reflected light spot changes according to the relative position of the recording track of the disk 1 and the light beam spot in the disk radial direction, and the difference between the outputs of the divided light receiving element areas a1 and a2. As a result, a tracking error signal can be detected. This detection method is called a push-pull method or a far-field method, and is widely used in optical disk devices.

The wobble signal is detected as described above. Since the wobble signal is FM-modulated, it has a frequency component centered on the FM carrier frequency. In order to extract this frequency component, the signal passes through a band-pass filter 8 having the average frequency (FM carrier frequency) of the reproduced wobble signal as the center frequency of the pass band. Based on the output, the address demodulator 9 performs FM demodulation and biphase demodulation. And extract address information.

[0012]

However, the above-mentioned conventional information reproducing apparatus has a problem that a signal-to-noise ratio (hereinafter abbreviated as S / N ratio) of a wobble signal cannot always be sufficiently ensured. . This will be described below.

The wobble signal detected as shown in FIG. 3 contains various noise components other than the wobble component which is a minute meander of the original track. The main noise factors include the effects of dropouts such as scratches, dust, and fingerprints on the disk surface, and the effects of crosstalk between adjacent tracks. Especially when the focus of the light beam spot is defocused, the diameter of the light beam spot on the recording surface increases,
The crosstalk of the wobble component of the adjacent track increases. In order to remove such unnecessary noise as much as possible, it is necessary to increase the frequency selectivity Q of the band-pass filter 8 to obtain a steep frequency characteristic. However, since the wobble signal is FM-modulated, the wobble signal includes not only the FM carrier frequency component but also a frequency component (deviation component) having a certain spread around the carrier frequency. If the selectivity Q is too large, even the deviation component which is the original wobble signal component is lost. Also, there is a variation in the linear velocity of the disk (in the MD, a linear velocity variation of about ± 7% is allowed according to the specification of the disk), and a certain pass band width is required. Further, in general, as the selectivity Q increases, the influence of variations in circuit element constants (capacitance C and resistance R) on the frequency characteristics increases as the selectivity Q increases. It is not preferable to make the degree Q too large. For these reasons, the selectivity Q of the band-pass filter cannot be made too large, and it is difficult to always ensure a sufficient S / N ratio of the wobble signal.

The present invention solves the above-mentioned conventional problems, and effectively eliminates unnecessary noise components without increasing the selectivity Q of the band-pass filter, thereby reducing the wobble signal S.
An object of the present invention is to improve the / N ratio and enable a more stable reproduction operation.

[0015]

In order to achieve this object, an information reproducing apparatus according to the present invention sets the center frequency of the pass band of the band-pass filter higher than the average frequency of the information signal read by the signal reading means. Set higher.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an information reproducing apparatus for reproducing an information signal from a disk on which an information signal modulated by a predetermined modulation method is recorded in a predetermined track form, wherein the rotation of the disk is performed. Rotation control means for controlling the number or linear velocity to a predetermined target value, signal reading means for reading the information signal from the disc, and a band pass for passing a desired frequency band with an output signal of the signal reading means as an input A filter, and demodulating means for demodulating the information signal based on an output of the band-pass filter, and a center frequency of a pass band of the band-pass filter, the average frequency of the information signal read by the signal reading means. Set higher than the frequency.

Hereinafter, an information reproducing apparatus according to an embodiment of the present invention will be described.

The main components of the information reproducing apparatus according to the embodiment of the present invention are the same as those shown in FIG.
Is the same as That is, when reproducing the ADIP signal from the disk 1 on which the bi-phase-modulated and FM-modulated ADIP signal is recorded in a predetermined track form (wobble), the rotation speed or the linear velocity of the disk 1 is controlled to a predetermined target value. Signal reading means comprising an optical pickup 6 for reading an ADIP signal from the disk 1 and a wobble signal detecting means 7, a band-pass filter 8 for limiting the output of the signal reading means, and a band-pass filter 8. And an address demodulating means 9 for demodulating the ADIP signal based on the output of the above. The difference between the information reproducing apparatus according to the embodiment of the present invention and the conventional information reproducing apparatus is the frequency characteristic of the bandpass filter 8.
This will be described below with reference to FIG.

FIG. 1 is a frequency characteristic diagram showing the frequency components of the input signal to the band-pass filter 8 and the frequency characteristics of the band-pass filter 8, wherein the horizontal axis represents the frequency and the vertical axis represents the amplitude. FIG. 1C shows the frequency components of the input signal to the band-pass filter 8, S denotes the amplitude of the wobble signal component, fs denotes the average frequency thereof, N denotes the amplitude of the unnecessary noise component, and fn denotes the average thereof. The typical frequency. FIG.
FIG. 1B shows the frequency characteristics of the band pass filter 8 of the conventional information reproducing apparatus, and FIG. 1A shows the frequency characteristics of the band pass filter 8 of the information reproducing apparatus according to the embodiment of the present invention. F0b in FIG. 1B is the center frequency of the pass band of the bandpass filter 8 of the conventional information reproducing apparatus, and FIG.
F0a indicates the center frequency of the pass band of the band pass filter 8 of the information reproducing apparatus according to the embodiment of the present invention. FIG.
The arrow labeled SNb in (b) schematically shows the S / N ratio when the bandpass filter characteristic of the conventional information reproducing apparatus is used, and the arrow labeled SNa in FIG. 5 schematically shows the S / N ratio when the band pass filter characteristic of the information reproducing apparatus according to the embodiment of the present invention is used.

In the conventional information reproducing apparatus, as shown in FIG. 1B, the center frequency f0b of the pass band of the band-pass filter 8 is set to be equal to the average frequency fs of the wobble signal component at the time of reproduction. (F0b０f
s). Thereby, the amplitude of the wobble signal component is maximized, and the S / N ratio is maximized assuming that the frequency components of the unnecessary noise are uniform. However, in practice, as shown in FIG. 1C, the unnecessary noise component (N) is often concentrated on the low frequency side of the wobble signal component (S). This will be described in detail below.

The main noise generation factors for the wobble signal include scratches on the disk surface, dust, dropout due to fingerprints, crosstalk components of adjacent tracks, and the like. First, considering the effect of dropout, the diameter of the light beam spot is 1-2 μm on the disk recording surface.
However, the thickness of the disk protective layer (about 1.2
mm) on the surface. Therefore, a dropout sufficiently smaller than 1 mm on the disk surface is hardly detected as reflected light of the light spot. As a result, the effect of dropout is concentrated on relatively low frequency components, and is generally about 500 Hz to 3 kHz for MD, CD (compact disc), DVD and the like. When the MD is reproduced at a normal linear velocity, the fundamental frequency of the wobble component (the carrier component of the FM modulation) is about 22.05 kHz, so that the noise component due to the dropout is concentrated in a lower band.

Next, considering the influence of the crosstalk of the adjacent track, the crosstalk of the adjacent track is caused by the fact that the light beam spot condensed on the recording surface of the disk is caused by the residual error of the focus servo system and the non-uniformity of the semiconductor laser and the objective lens. This is a phenomenon in which the wobble component of an adjacent track is picked up due to point aberration or the like, which spreads in the disk radial direction. The MD wobble signal is recorded at a constant linear velocity (CLV), and the physical length at which the wobble is repeated is constant regardless of the disk radial position. That is, when two adjacent tracks are simultaneously reproduced at a predetermined number of revolutions, the frequency of the wobble component reproduced from the two tracks slightly shifts, and a beat component corresponding to the difference between the two frequencies is generated. In the MD, since the frequency difference is about several Hz, it can be seen that the noise component due to the crosstalk is also in a band much lower than the fundamental frequency of the wobble component.

If the unnecessary noise component of the input signal to the bandpass filter is concentrated on the lower side than the average frequency of the wobble signal component, as shown in FIG. At the center frequency of the wobble signal component (f0b ≒ f
1 (a), the center frequency of the pass band of the band-pass filter is shifted slightly higher than the average frequency of the wobble signal component (f0a> fs) as shown in FIG.
The S / N ratio can be improved. (SNb> SNa)
This is because the frequency characteristic of the bandpass filter is generally
This is because the inclination is relatively gentle near the center frequency of the pass band, and becomes steeper as the distance from the center frequency increases. Therefore, as shown in FIG. 1A, when the center frequency of the pass band of the band-pass filter is set higher than the average frequency of the wobble signal component (f0a> f)
s), while the amplitude of the wobble signal component (S) is slightly reduced, the amplitude of the low-frequency noise component (N) is significantly reduced, and as a result, the S / N ratio can be improved.

As described above, according to the information reproducing apparatus of the embodiment of the present invention, the center frequency (f0a) of the pass band of the band-pass filter is set to the average frequency of the wobble signal component read by the signal reading means. By setting higher than (fs) (f0a> fs), the S / N ratio of the wobble signal can be improved, and the stability of the reproduction operation against dropout, crosstalk, etc. can be improved.

In the embodiment of the present invention, an MDIP (address in pre-groove) signal demodulation device for a MD (mini-disc) is used, but it is widely used for optical disks, magneto-optical disks, magnetic disks, and the like. It is applicable not only to address information but also to any range for reproducing information signals modulated and recorded on a disc, such as music information, video information, and other digital information. It is applicable and there is no change in the spirit of the present invention.

Further, the band pass filter of the present invention can be realized by an analog circuit, a digital circuit, or software.

In the embodiment of the present invention, the rotation of the disk is controlled by directly detecting the number of rotations of the motor with the FG. However, the signal reproduced from the disk (from the reproduction signal) is used without using the FG. By comparing a self-clock signal extracted by a PLL or the like or a reproduction sector signal indicating the head of a sector which is a recording unit of information with a predetermined reference signal, rotation control is performed so as to have a constant linear velocity (CLV). May be.

[0028]

As described above, the information reproducing apparatus according to the present invention sets the center frequency of the pass band of the band-pass filter to
By setting the frequency higher than the average frequency of the information signal read by the signal reading means, the S
/ N ratio can be improved, and the stability of reproduction operation against dropout, crosstalk, and the like can be improved.

[Brief description of the drawings]

FIG. 1 is a frequency characteristic diagram for explaining a frequency characteristic of a band-pass filter of an information reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a state of a minute wobble of an MD track.

FIG. 3 is a schematic diagram showing a general method of detecting a tracking error component.

FIG. 4 is a block diagram showing main components of an information reproducing apparatus according to a conventional and an embodiment of the present invention;

[Explanation of symbols]

 2 Motor 5 Rotation control means 6 Optical pickup 7 Wobble signal detection means 8 Band pass filter 9 Address demodulation means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D044 BC05 BC06 CC04 FG01 FG16 FG19 5D090 AA01 BB03 BB10 CC04 DD03 DD05 EE12 EE17 EE18 FF25 GG09 GG22 GG28

Claims (1)

[Claims] 1. An information reproducing apparatus for reproducing an information signal from a disk on which an information signal modulated by a predetermined modulation method is recorded in a predetermined track form, wherein the number of rotations or the linear velocity of the disk is set to a predetermined value. A rotation control unit for controlling the target value of the signal, a signal reading unit for reading the information signal from the disk, a band-pass filter that receives an output signal of the signal reading unit and passes a desired frequency band, Demodulating means for demodulating the information signal based on an output of the filter, wherein a center frequency of a pass band of the band-pass filter is set higher than an average frequency of the information signal read by the signal reading means. An information reproducing apparatus characterized by the above-mentioned.